ActewAGL estimates about 6000 customers across the ACT and NSW have been caught up in the breach.

The bills appear to have been bundled by postcode and then, for reasons that remain unclear, were sent in boxes and envelopes addressed to specific customers.

Customers have had their personal information sent to addresses in Belconnen, Gungahlin, Chisholm, Calwell, Kingston, Palmerston and Wanniassa, as well as a city post box.

The Canberra Times is aware of nine separate incidents, including bills being sent to Belconnen resident John Steep, who received an envelope containing hundreds of them on Wednesday.

On Thursday, eight more people came forward with similar stories.

The utility provider has told recipients of the bundles to wait for them to be collected by ActewAGL representatives, but one recipient has returned the bundle to an ActewAGL shopfront.

Mr Steep, who contacted ActewAGL to return the bundle of documents he received at his Belconnen home on Wednesday, said the almost half-ream of outstanding bills had not been collected as of Thursday afternoon.

The bills in Mr Steep's bundle were addressed to ActewAGL customers in the 2617 postcode, which covers the suburbs of Belconnen, Kaleen, Giralang, Evatt, McKellar, Bruce and Lawson.

Several bills were addressed to houses on Mr Streep's street and other nearby homes.

ActewAGL told Mr Steep on Thursday morning it had sent people out to collect the bills at 6.45pm on Wednesday, which was right after Mr Steep and his wife had gone out for a walk.

He was told that they arrived in the evening to collect the bills because the ActewAGL representatives had other things to do first.

An ActewAGL staff member also told Mr Steep that the utility provider was unlikely to send anyone to retrieve the bills on Thursday due to safety concerns about driving in the rain and on wet roads.

"I'm stunned. It suddenly becomes my problem. It's not funny any more," Mr Steep said.

Mr Steep said ActewAGL had told him on Thursday evening the bills would be collected on Friday morning.

Mr Steep first contacted ActewAGL about the mistaken delivery just before midday on Wednesday.

"I didn't want to look like I was sitting on it," he said.

Mr Steep was initially told at 1.20pm on Wednesday that two representatives from the utility provider would collect the cache of bills within about an hour.

"I'm just cranky that I've wasted a day on this," Mr Steep said.

Belconnen resident Samantha Simms received a box containing more than 500 ActewAGL electricity bills addressed to houses in the 2617 postcode sometime between 5.30 and 7pm on Wednesday.

"It was really concerning. I was glad my bill was the one in the envelope [attached to the box]," she said.

A resident in Chisholm was sent a box containing between 200 and 300 outstanding gas bills addressed to customers in Chisholm and Calwell. They had not been collected by Thursday night.

2CC program director Peter Davidson received a bundle of about 150 Icon Water bills on Wednesday, addressed to homes in Gungahlin and Belconnen.

Mr Davidson rang Icon Water at 4.30pm on Wednesday and was told to return the bills to sender. At 10am on Thursday, he contacted the water provider again and was told someone would be sent out to collect them but no collection time had been arranged.

"The guy on the other end was pretty blasé about the whole thing," Mr Davidson said.

Palmerston resident Larry Appley received 21 electricity bills, addressed to houses in Nicholls, Ngunnawal and Charnwood.

"Being a major breach of privacy as it is, I expected someone would ring me back in 15 minutes. But I heard nothing," he said.

An ActewAGL staff member contacted Mr Appley after he posted a picture of the bills to the company's Facebook page on Thursday evening.

A bundle of about 20 bills addressed to ActewAGL customers in Kingston was also delivered to an employee of The Canberra Times on Wednesday, but was not found until Thursday morning.

An envelope containing 19 electricity bills was sent to a post box at the Canberra general post office, which included bills addressed to post office boxes in Braddon, the city and Belconnen.

A Calwell resident also received an envelope that contained 13 Icon Water bills on Thursday. The resident was told the envelope would be collected on Thursday morning.

Jacquelyn Lamont of Wanniassa received an A4 envelope with seven electricity bills on Wednesday, including her own. ActewAGL told her they would send someone over to collect them, but the bills remained uncollected on Thursday evening.

The six other bills in the envelope were all addressed to houses within the 2903 postcode.

"They didn't seem too concerned," Ms Lamont said. "I'm so annoyed with them."

The large bundles had the recipients' bills in an envelope taped to the outside of the larger package.

The bills contained names and addresses of ActewAGL customers, unique reference numbers and show how much gas the customer were using. In some cases, it could have been possible to determine from the bill if a person was receiving a pension.

ActewAGL supplies gas to about150,000 customers in the ACT.

A spokeswoman for ActewAGL said the company was investigating the mail out error.

"[This] has resulted in invoices that we prepare for ActewAGL and Icon Water customers being received in sealed envelopes by someone other than the intended recipient," she said.

ActewAGL said it had put on hold mail being handled by an external provider after it was notified of the mistake.

"We are investigating the matter in accordance with our internal procedures, which reflect the guidelines publicly issued by the Privacy Commissioner’s office," the spokeswoman said.

The company confirmed on Thursday that it had begun contacting affected customers and would extend bill payment times. The utility provider said it had also alerted the Privacy Commissioner's office.

Agencies subject to the Privacy Act, which include ActewAGL, must take reasonable steps to prevent misuse, interference or loss of any personal information they hold.

"We apologise for any inconvenience or concern caused," a company spokeswoman said.

Icon Water said ActewAGL managed billing processes for the water provider and that it was aware of the issue and working closely with ActewAGL to investigate the mail out error.

"Our customers’ privacy is of the utmost importance. Distribution of bills was suspended as soon as the issue was identified," the company said in a statement.

"ActewAGL has begun contacting known affected customers and collecting misdirected mail," the company said on Thursday.

The Australian Competition and Consumer Commission's Scamwatch website advises people to lock their mailboxes and destroy any documents containing personal information before disposing of them.

Scammers can use private information obtained through discarded personal documents, including utility bills, to commit identity theft.